The invention relates to a circuit arrangement for generating a preset first number of output pulses, having a substantially equal interspacing, between two input pulses having a variable interspacing, under the control of clock pulses which have a cycle duration which is constant at least in the short term, but considerably smaller than the interspacing of the output pulses.
Such a circuit arrangement essentially provides frequency multiplication and may be built up, for example, as a phase-coupled loop comprising a voltage-controllable oscillator whose output pulses are divided by the preset number by means of a counter and are compared in phase with the input pulses, the result of the comparison controlling the frequency of the oscillator via a low-pass filter. Such a phase-coupled loop may be of analog or digital design. If then the frequency of the input pulses, i.e. the distance between two consecutive input pulses, is changed, the frequency of the oscillator is so corrected that the number of output pulses between two consecutive input pulses again corresponds to the preset number. This correction, however, takes place with a delay owing to the action of the low-pass filter, and the total number of generated output pulses between several consecutive input pulses may temporarily considerably deviate from the value corresponding to the preset first number, i.e. in dependence on the time characteristic of the change in the input frequency and the dimensioning of the low-pass filter. In many applications, however, it is necessary for the number of output pulses to correspond to the preset first number as quickly as possible. This problem arises, for example, in a matrix printer which is to print various printing rasters with a very high repetition accuracy also over the entire printing width. A common divider must then be present for all occurring printing rasters, i.e. a clock signal having a correspondingly high frequency whose single pulses are coupled to the position of the print head with the highest possible exactness. Scanning of the print head position immediately at the print head is necessary for a high positioning accuracy of the single print dots, since otherwise the natural dynamics of the print head drive directly and negatively influence the accuracy. The direct generation of a fine raster rhythm corresponding to the common divider by a scanner element, which is moved together with the print head over a ruler positioned along the horizontal print path, is technically difficult and very expensive. Scanning of the print head position is accordingly only practicable with a comparatively rough subdivision. The corresponding finely divided raster pulses must then be generated from these roughly divided raster pulses with the resolution required by the common divider. These fine raster pulses must have a high accuracy as to their position and especially as to their total number as well as a strict relation to the rough division, so that the locations where printing starts in the print positions correspond as exactly as possible in consecutive print lines.